Can I "borrow" rocker arms from my '65 273 for my '71 340?

-
dibbons

dibbons

Well-Known Member
Joined
Nov 6, 2009
Messages
5,828
Reaction score
3,893
Location
La Paz, B.C.S., Mexico
What is involved in replacing factory 1971 340 rocker arms with adjustable rocker arms from a 1965 two barrel 273 with a factory solid camshaft ? My 340 will still run the hydraulic camshaft, but I like the idea of being able to adjust the valve train after I deck the 340 block, mill the cylinder heads, etc., etc.
 
You will need to measure for new pushrods.
 
Is there any difference in geometry using the adjusters on the rocker arms vs. making the push rods longer/shorter?
 
dibbons said:
Is there any difference in geometry using the adjusters on the rocker arms vs. making the push rods longer/shorter?
Click to expand...

We would not be telling to get new pushrods otherwise.
 
dibbons said:
Is there any difference in geometry using the adjusters on the rocker arms vs. making the push rods longer/shorter?
Click to expand...
Nothing in the geometry of the rockers. Just where the push rods sit in the Hyd. lifters is different then the solid lifters., necessitating the use of different length pushrods, and the ones you need are Cup on one end and ball on the other. Non adj. valvetrain uses ball and ball.
 
Also, the 273 shafts were not designed to be run with hydraulic cams. If you do use a hydraulic cam on 273 shafts make sure you put a groove in the shaft under the rocker. When there is no lash, there is not enough clearance and the rocker will gall the shaft.
 
Never thought about galling. Anyone seen the 1970 340 TA heads with factory adjustable rockers and hydraulic camshaft? I wonder what those rocker shafts looked like?
 
dibbons said:
Never thought about galling. Anyone seen the 1970 340 TA heads with factory adjustable rockers and hydraulic camshaft? I wonder what those rocker shafts looked like?
Click to expand...

They were grooved and originals are worth more than gold. I have actually seen a few originals come apart for the first time.
 
I would not "just throw out" a part number for this in a million years. The only right way to do it is measure.
 
"I have actually seen a few originals come apart for the first time."

What do you mean by come apart, failed, broke, or you just got a peek at 'em?
 
RustyRatRod said:
I would not "just throw out" a part number for this in a million years. The only right way to do it is measure.
Click to expand...

X 2 measure twice and order once. I recently swapped solid cams in my 340. Went few sizes bigger, I had stock length 273 pushrods for a solid cam and 273 rockers on the old cam. You would THINK I could reuse the pushrods but the base circle on the new cam was bigger, had to measure and buy a new set of pushrods.
 
dibbons said:
Never thought about galling. Anyone seen the 1970 340 TA heads with factory adjustable rockers and hydraulic camshaft? I wonder what those rocker shafts looked like?
Click to expand...
Plus T/A rockers are offset on the intake.....
 
RustyRatRod said:
I would not "just throw out" a part number for this in a million years. The only right way to do it is measure.
Click to expand...

We just measured ours and went with a custom length...

Eddy Pushrod F01AA.jpg
 
Marcohotrod said:
with hydraulic lifters and adjustable rockers - many times a custom pushrod is not needed
Click to expand...

I agree there is a good chance the pushrods you mentioned will work, but why not measure to be sure? I hate sending back parts
 
To take advantage of the best geometry, you should only have a few threads, as I remember, showing at the bottom of the adjusting screw. Measure after all machine work and assembled. As RRR said then order custom pushrods, unless you get real lucky.
 
I tried to use 273 cast rocker on my 360 Engine with RHS LA heads and the rockers were hitting the valve springs retainers so that was a no go for me. Maybe because my valve springs are wider that stock ones? Also I tried a Crane ductile iron set and they hit too, less but enough to make it a no go.

I had to put cheap Proform rocker since it was the only thing that I have in hand, but I'm not confident with them, I will move to Comp Cams Magnum Steel Rocker as soon I can spend the cash. For now I'll have to stick with the Proform, only thing that I did for peace of mind was to replace the locknuts for with a Crane set.
 
Marcohotrod said:
with hydraulic lifters and adjustable rockers - many times a custom pushrod is not needed
Click to expand...

Really? I have seen adjustable rockers with hydraulic lifters take anywhere between a 7.05" to an over 7.5" pushrod. No way in the world I would try it without measuring first. Just too many variables, not the least of which was Chrysler's absolute terrible deck height finishing. Most were way too high.

Then, throw the engine's history in the mix.......you're talkin about up to a 50 year history. No telling what machine work has been done previously, what thickness head gaskets, what lifters you're using......and on and on.

The optimum adjustment is to have between 1-3 threads protruding through the rocker arm on the pushrod side. With too long a pushrod, there is the chance that the top of the pushrod cup will contact the rocker and result in broken parts.

With too short a pushrod, there is a chance the adjuster ball will break off from too much length with the pushrod having too much angle on it.

No sir. The best thing to do is measure, measure, measure. And get it RIGHT.
 
Last edited:
We tried to order off the shelf push rods for our build with 273 rockers in a 340, and they all ended up too long...

We ended up measuring and going custom order...
 
RustyRatRod said:
Really? I have seen adjustable rockers with hydraulic lifters take anywhere between a 7.05" to an over 7.5" pushrod. No way in the world I would try it without measuring first. Just too many variables, not the least of which was Chrysler's absolute terrible deck height finishing. Most were way too high.

Then, throw the engine's history in the mix.......you're talkin about up to a 50 year history. No telling what machine work has been done previously, what thickness head gaskets, what lifters you're using......and on and on.

The optimum adjustment is to have between 1-3 threads protruding through the rocker arm on the pushrod side. With too long a pushrod, there is the chance that the top of the pushrod cup will contact the rocker and result in broken parts.

With too short a pushrod, there is a chance the adjuster ball will break off from too much length with the pushrod having too much angle on it.

No sir. The best thing to do is measure, measure, measure. And get it RIGHT.
Click to expand...


The actual measurement for adjuster protrusion (taking into account the rockers have the factory oil hole timing) is 9/32" +/- .020 and the more agressive the lobe the more important this is.

Pushrod length does NOT affect rocker arm geometry per se, as the only thing that controls geometry on a shaft is the relationship of the valve to the height of the stand, and the rocker itself. Lift factors in, but en talking about correcting geometry, you either raise or lower the shaft, or make the valve longer or shorter. The push rod length just affects how far out the adjuster is.

That said, some rockers have the adjuster at a different angle than OE, so as you screw the adjuster up and down it SLIGHTLY changes the rocker arm ratio.
 
You must log in or register to reply here.
-

Back
Top